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.\" Common Development and Distribution License ("CDDL"), version 1.0.
.\" You may only use this file in accordance with the terms of version
.\" 1.0 of the CDDL.
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.\" source.  A copy of the CDDL is also available via the Internet at
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.\" Copyright 2016 Joyent, Inc.
.\"
.Dd June 02, 2016
.Dt MAC_LSO_GET 9F
.Os
.Sh NAME
.Nm mac_lso_get
.Nd get LSO information on message blocks
.Sh SYNOPSIS
.In sys/mac_provider.h
.Ft void
.Fo mac_lso_get
.Fa "mblk_t *mp"
.Fa "uint32_t *mss"
.Fa "uint32_t *flags"
.Fc
.Sh INTERFACE LEVEL
illumos DDI specific
.Sh PARAMETERS
.Bl -tag -width Fa
.It Fa mp
A pointer to a
.Xr mblk 9S
structure that contains an outgoing frame.
.It Fa mss
A pointer to a value that will be filled in with the maximum segment
size (MSS).
.It Fa flags
A pointer to a value that will be filled in with various flags that
indicate the behavior to perform.
.El
.Sh DESCRIPTION
The
.Fn mac_lso_get
function is used by device drivers that have indicated that they support
the
.Sy MAC_CAPAB_LSO
capability to determine whether large send offload (also known as large
segmentation offload or LSO) is required for this frame or not.
If so, the driver should take the appropriate actions to program the hardware
to perform LSO.
.Pp
The
.Fn mac_lso_get
function should only be called on the first
.Sy mblk_t
that begins a given individual frame in a chain.
In other words, it only works on entries where it is the first of many possible
entries linked together by the
.Sy b_cont
member.
The first
.Sy mblk_t
received from any
.Xr mac 9E
API or pointed to by a
.Sy b_next
pointer should be used.
.Pp
A device driver should first look at the
.Fa flags
argument to determine what to do.
.Fa flags
may be a bitwise inclusive OR of the following:
.Bl -tag -width Sy
.It Sy HW_LSO
This flag indicates that hardware needs to perform segmentation
offload.
The maximum segment size that the driver should use is available through the
.Fa mss
argument.
.El
.Sh CONTEXT
The
.Fn mac_lso_get
function may be called from
.Sy user ,
.Sy kernel ,
or
.Sy interrupt
context.
.Sh SEE ALSO
.Xr mac 9E ,
.Xr mblk 9S
